huangyhg

rain fall on rcc (reinforced cement concrete) slab
hi,
this question is for a temple construction in gujarat province of india. my brother is managing one project of temple construction there.
he just finished a rcc (reinforced cement concrete) slab and just after casting a slab a heavy rain fall on slab for about half an hour. can you please advise what remedial measure can be taken now?
how we can save this slab? what kind of damage may occur?
waiting for your earliest reply.
thanks,
atul
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it sounds like when it rained the concrete was still wet. the problem with this is, the concrete now has too much water. which means-
1. the durability of the slab now is in question.
2. the concrete will not be able to achieve its design strength.
3. the rainfall must have created open path in the concrete where the rain water seeped thru the slab. this only means the slab is now porous.
4. the reinforcement will rust out pretty quickly.
as a remedy, you probaly can remove the slab and start over. next time try to keep it covered.
....or possibly the top area of the slab thickness has been ruined and you could potentially grind off these top layers and then bond a topping slab to the remaining lower segments of the slab thickness. this would be predicated on:
1. knowing how deep the damage goes (cores and applicable material analysis...expensive)
2. the availability of local contractors to grind the slab...have they the right equipment to do it right without damaging the lower layers.
3. the availability of bonding agents to use.
4. the function of the slab - if it is just for an interior living space, perhaps ok to do this. if it is for a high performance warehouse slab with forklift traffic, etc., then maybe the bonded topping wouldn't be a good idea.
the extent of damage due to rain is probably very thin, 1/4" to 3/4" maximum. a bush hammer can be used to remove the weak layer and then a bonding agent and a repour of the surface can be effected. if the thickness can be lessened, then just grinding smooth and a coating of epoxy will also give satisfactory results.
i am sure that he is saying that the concrete was still wet when it rained. i do not think that all the water evaporated then and there, what happen to the rest. some of the rest got mixed with the slab concrete and rest found its way thru the slab and into the ground below. so, how this slab can be saved without loosing its durability and serviceability?
jae has given you good advice. the slab will have been affected in differing degrees depending on the time since placement. if finishing had commenced in some part of the slab, the structural integrity of that part is not likely to have been affected. where the concrete was still plastic, the top part of the slab will have been adversely affected, but in varying amounts.
did the finishing process occur yet? or did they just screed and float the concrete when the rain fell? if the finishing was complete, the rain could be considered ponding for curing purposes.

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